1. Field of the Invention
The present invention relates to a magnetostatic wave filter, and specifically relates to a magnetostatic wave filter using ferrimagnetic base material, for example, a YIG (Yttrium, Iron, Garnet) thin film.
2. Description of the Prior Arts
FIG. 3 is an illustrative view showing an example of the conventional magnetostatic wave filter. In this magnetostatic wave filter 1, a GGG (Gadolinium, Gallium, Garnet) substrate 3 is installed on a grounded conductor 2, and a YIG thin film 4 is formed on this GGG substrate 3. Furthermore, on the YIG thin film 4, an input antenna 5a and an output antenna 5b each consisting of a wire are formed in parallel with a space therebetween.
FIG. 4 is an illustrative view showing another example of the conventional magnetostatic wave filter. In this magnetostatic wave filter 1, in comparison with the conventional example as shown in FIG. 3, particularly, another YIG thin film 6 is formed on the YIG thin film 4 so as to cover the input antenna 5a and the output antenna 5b. Furthermore, a separate GGG substrate 7 is formed on this YIG thin film 6.
FIG. 5 is an illustrative view showing still another example of the conventional magnetostatic wave filter. In this magnetostatic wave filter 1, in comparison with the conventional example as shown in FIG. 3, particularly, the GGG substrate 3 is mounted on the inner bottom of a hollow cylindrical cavity 8 consisting of metal. Then, two coaxial connectors 9a and 9b are installed on the side surface of this cavity 8, and the input antenna 5a and the output antenna 5b are connected to the core conductors of these coaxial connectors 9a and 9b, respectively.
In this magnetostatic wave filter as shown in FIG. 3 and the magnetostatic wave filter as shown in FIG. 4, the amount of attenuation of the attenuation band thereof is not so large due to electromagnetic wave transmitted from the input antenna directly to the output antenna.
On the other hand, in the magnetostatic wave filter as shown in FIG. 5, as the frequency characteristic thereof is shown in FIG. 6, spurious radiation is generated by a resonance mode of the cavity.